1. Field of the Invention
The invention generally relates to an optical device, and more particularly, to a projection lens with high imaging quality and a projection device using the projection lens.
2. Description of Related Art
Among many types of display devices, the projection device features a smaller device volume but producing a large-size image frame with an area several times of the surface area thereof, so that the projection device in the display field has un-replaced advantage. The projection device projects an image beam converted by a light valve through a projection lens onto a screen. Therefore, the quality of the image frame is largely affected by the quality of the projection lens. In this regard, the projection lens is a crucial optical component in the projection device.
In general speaking, the wide-angle projection lens is able to shorten the distance between the screen and the projector device, and at the same time to get the large-size image. However, the wide-angle projection lens known in the art will produce a variety of aberrations such as distortion or field curvature, and makes the quality of the image projected by the projection device poor.
In the known art, a variety of methods to improve the imaging quality of the wide-angle projection lens are disclosed. U.S. Patent Application No. US20040233394 discloses a scheme that a reflector is added into the projection lens to shorten focal length and reduce the aberration. U.S. Pat. No. 7,009,765 uses a secondary imaging principle to produce an intermediate image, thereby reduce the aberration problem. U.S. Pat. Nos. 5,477,394, 6,994,442, 6,989,936, 6,690,517 and 6,984,044 disclose a scheme that by using a plurality of reflectors to shorten the projection distance. U.S. Patent Application No. US20110002051A1 uses two aspheric lenses and a curved-surface reflector to correct the aberration. U.S. Pat. Nos. 6,896,375, 7,341,353, 7,545,586 and 7,567,380 use multiple reflectors to shorten the focal length. U.S. Pat. No. 7,150,537 and U.S. Patent Application No. US20100172022A1 use positive-negative distortions complementary principle of two groups of lenses to correct the aberration. U.S. Pat. Nos. 4,427,274 and 5,495,306 propose a projection lens. U.S. Pat. No. 8,081,377 discloses a projection lens with an intermediate image. U.S. Patent Application No. US20100171937 discloses an optical system used in a projection-type display device. U.S. Pat. No. 6,542,316 discloses a wide-angle projection lens.